The present disclosure relates to a semiconductor light-emitting device and a method for manufacturing the same, and more particularly to a semiconductor laser device using a nitride semiconductor and a method for manufacturing the same.
A III-V group nitride compound semiconductor such as gallium nitride (GaN), so-called a “nitride semiconductor”, has been drawing public attention. The general formula of nitride semiconductors can be expressed as InxGayAl1-x-yN (0≦x≦1, 0≦y≦1, x+y≦1). A nitride semiconductor is a compound semiconductor containing aluminum (Al), gallium (Ga) and indium (In) which are III-group elements and nitrogen (N) which is a V-group element. In the field of optical devices, light-emitting diodes (LEDs) using nitride semiconductors have been used as elements of large-size display devices, traffic lights, etc. While some white LEDs employing a combination of LEDs using nitride semiconductors and phosphors have been commercialized and, if the light-emitting efficiency is improved, are expected to replace existing lighting devices.
On the other hand, semiconductor laser devices in the blue-violet to pure-green region using nitride semiconductors have also been very actively researched and developed. With a blue-violet semiconductor laser device, the spot diameter on an optical disc can be reduced as compared with semiconductor laser devices emitting light in the red or infrared range used in conventional optical discs such as compact discs (CDs) and digital versatile discs (DVDs), and it is therefore possible to improve the recording density of an optical disc. Pure-blue laser devices whose light-emitting wavelength is 450 nm to 470 nm and pure-green laser devices whose light-emitting wavelength is 525 nm to 535 nm can be used in backlight applications for laser displays and LCDs. By using these, it is possible to realize displays having very high color reproducibility as compared with conventional displays.
Particularly, pure-blue and pure-green laser devices, among these nitride semiconductor laser devices, have a very high oscillation threshold current, and are therefore yet to be commercialized. Generally, in order to obtain a nitride semiconductor laser device whose light-emitting wavelength is 430 nm or more, it is necessary to increase the indium content of the well layer in the active layer having a quantum well structure. This is because it is necessary for increasing the light-emitting wavelength to increase the indium content of the well layer and to reduce the energy band gap of the well layer. For crystal growth of a well layer having a high indium content, it is necessary to increase the concentration of the indium material in the gas phase. However, if the indium concentration in the gas phase is increased during crystal growth, indium which is not taken into the well layer segregates on the surface of the well layer. Regions where indium segregates on the surface become non-light-emitting regions, thereby significantly lowering the light-emitting efficiency of the active layer. In a well layer with a high indium content, indium content non-uniformity is also likely to occur in addition to the indium segregation. This results in a large photoluminescence half width. As the photoluminescence half width is larger, it is more difficult to obtain a gain to reach laser oscillation.
Methods have been studied in which in order to suppress the indium segregation in the well layer, the growth is once discontinued after the crystal growth of the well layer, and a carrier gas containing an ammonia gas, a nitrogen gas and a hydrogen gas is supplied to remove segregated indium (see, for example, Japanese Laid-Open Patent Publication No. 2009-054616).